Height-adjusting mechanisms of the aforesaid type, wherein the height of the chair seat is adjusted by rotation of the chair seat when unoccupied, with the adjusting mechanism being disengaged when the chair seat is occupied, are well known and such mechanisms are widely used on spindle-type office chairs. In mechanisms of this general type, the spindle is threadably engaged with a nut which can be suitably held in nonrotatable relationship relative to either the base or the chair seat so as to define adjusting and nonadjusting positions. A spring normally urges the chair seat slightly upwardly when it is unoccupied so that the nut is nonrotatably connected to the base, whereby rotation of the seat causes the spindle to threadably move through the nut and hence cause a height adjustment of the seat. Conversely, when the chair seat is occupied, the external force imposed on the chair seat overcomes the spring and moves the chair seat and spindle downwardly a limited amount so that the nut is nonrotatably engaged with the spindle, whereby swivelling or rotating the occupied chair seat does not change its height. Height-adjusting mechanisms of the above type are illustrated by U.S. Pat. Nos. 3,870,271 and 3,991,965.
While these known height-adjusting mechanisms do perform in a generally satisfactory manner relative to the normal height adjustment throughout the selected adjustment range, nevertheless these mechanisms have been unsatisfactory when the unoccupied chair seat reaches the extreme limits of its height-adjustment range, such as when the unoccupied chair seat reaches its lowermost adjusted position. In these known mechanisms, when the seat is unoccupied, the nut is non-rotatably locked by its engagement with stops which are fixed to the base. Thus, when the chair seat is rotationally adjusted into its lowermost height position, any attempt to continue the rotation of the chair seat causes the nut and spindle to be tightly wedged together so that not only is further rotation of the chair seat impossible, but rotational release of the chair seat is difficult and the height-adjusting mechanism can be damaged.
Another disadvantage associated with the known height-adjusting mechanism, specifically those illustrated by the aforesaid patients, is the manner in which the spring is captivated within the mechanism. Specifically, the spring in the aforesaid mechanisms is captivated below the nut in such a manner that it is compressed into a solid height condition when the chair is adjusted into its lowermost height position, or in the alternative the spring is formed as resilient washers which continuously urge the spindle-mounted clutch washer against the nut so that during height-adjusting rotation of the unoccupied chair seat a continuous engagement-disengagement action occurs between the nut and clutch washer which not only increases the wear of these elements but also creates undesired resistance to rotation and an undesired clicking noise.
Still another disadvantage of known mechanisms is their mechanical complexity and bulkiness, and particularly their inability to be efficiently and compactly contained within the base pedestal.
Other examples of known height-adjusting mechanisms for chairs are disclosed in U.S. Pat. Nos. 4,026,509, 3,799,486, 3,218,021 and 2,702,075.
Accordingly, the present invention relates to an improved height-adjusting mechanism for a chair, namely a height-adjusting mechanism of the general type described above in that it permits a height-adjusting function to occur solely by rotation of the chair seat when the latter is unoccupied, which improved mechanism overcomes the above-mentioned disadvantages. In this invention, when the chair seat is adjusted into its uppermost or lowermost height positions, the mechanism still permits the chair seat to freely rotate or swivel.
In the improved height-adjusting mechanism of this invention, the threaded spindle as fixed to the chair seat is threadably engaged with a nut which is positioned adjacent and within a bore formed in the upper end of the base pedestal. A spring coacts between the base and nut and urges the nut, and hence the chair seat, upwardly whereby the nut is engaged with a clutch plate fixed to the pedestal. This clutch plate holds the nut nonrotatable so that when the chair seat is unoccupied and is rotated, the spindle threads upwardly or downwardly through the nut dependent upon the direction of rotation so as to adjust the height of the chair seat. The nut and clutch plate have opposed engageable cam portions which effect automatic disengagement therebetween if the engaged nut and clutch plate are subjected to an excessive torsional resistance. When the chair seat is occupied, the weight of same moves the nut downwardly away from the clutch plate into engagement with a clutch washer which is seated on the pedestal but is nonrotatably keyed to the spindle, whereby the chair seat and the accompanying spindle and nut can freely rotate or swivel as desired without causing a height adjustment to occur. The spindle has a limit structure associated therewith for defining the lowermost height position of the chair seat. This limit structure, in a preferred embodiment, comprises a tube of preselected length positioned in surrounding relationship to the spindle and having its lower end bearing on the nut, and its upper end positioned in close proximity to the underside of the chair seat. When the chair seat is adjusted into its lowermost height position, an abutment on the chair seat engages the upper end of the limit tube so that a reaction force is transmitted through the tube onto the nut, thereby preventing further rotation between the nut and spindle. If the chair seat is then rotated an additional amount in a direction tending to cause a downward adjustment, the opposed cam portions automatically cam the nut downwardly so that it disengages the clutch plate, thereby preventing any further lowering of the chair seat while at the same time permitting the chair seat to freely rotate to prevent binding between the spindle and nut. As the nut rotates, it revolves on the clutch plate so that the cams make a clicking sound which thus indicates that the chair seat is at its lowest position.
Other objects and purposes of the invention will be apparent upon reading the following specification and inspecting the accompanying drawings.